Replies

1. 
   frontiercc2 | Jan 15, 2008 08:09pm | #1

   "Last night it reached 25 degrees outside, I had the thermostat at 66. The air coming out of the registers feels just barely warm at best.
   The system runs for 21-30 minutes before cycling off, then kicks back on 5-7 minutes later.
   Also there are light bands of ice around the heat pump fins again."

   I'm no heat pump expert, but that all sounds pretty normal to me. Especially if you are not running the "emergency heat". At that temp, I have found the emergency heat to be necessary as the HP cannot keep up with the demand.

   It is also my understanding that having exceptionally dirty filters can cause them to freeze up as you described. And the low refrigerant level could certainly contribute to the problem.

   I don't think the issues are related. Charlotte doesn't typically see 25 degrees on a regular basis. The previous freezing up of the coils and the current inability of the HP to meet demand sound to me to be unrelated.

   But Like I said, I'm no expert.

   And contrary to popular opinion, I LOVE my Heat Pump. Especially with the spike in NG and Oil prices, while my electricity is fixed at 4.4 / kWh

2. 
   roger g | Jan 16, 2008 05:31am | #2

   Without going into refrigeration 101, heat pumps are supposed to ice up on the outside in the winter. After it ices up to some degree it goes into defrost mode. Sometimes, depending on the process it can be a bit noisey.

   Without looking at your unit I wouldn't know what was happening. For all I know it was working fine (though noisey) until someone added more refrigerant than needed. That could could give you no end of problems.

   Clean filters every month.

    

   roger

    

1. 
   Syma | Jan 16, 2008 06:47am | #3

   Thank you guys.The refrigerant was over charged or too much and the air handler was too cool? if I remember right.All seems ok for now (finger crossed) as I don't have $6-7K in the budget for a 15 SEER York 8T Series.I will repost if problems crop up again.Thanks

1. 
   roger g | Jan 16, 2008 06:29pm | #4

   Good luck. As an aside, an over charge of refrigerant doesn't make anything colder. It's the "right amount" that's crutial.

    

   roger

1. 
   DickRussell | Jan 16, 2008 07:36pm | #5

   To expand on the note that "It's the "right amount" that's crucial," the key things in any heat pumping design (refrigeration, A/C, heating) are the minimum temperature of the heat source, the maximum temperature of the heat sink (where the heat gets dumped), the choice of refrigerant, and the operating pressures thus required.For any particular refrigerant, its vapor pressure curve defines the pressure corresponding to any temperature where change between vapor and liquid phases occurs. This is an exponential relation, which curves up dramatically as temperature increases).Keep in mind that heat flows only from hot to cold. In the heat pump cycle, refrigerant is evaporated at some low pressure ("low" is relative here), on the curve, where the temperature is below that of the heat source. In the winter, this means below the coldest temperature at which the device is to be able to work. Just how far "below" is a tradeoff between cost of coil surface area and energy cost of compressing the evaporated refrigerant.The compression of the vapor refrigerant also increases its temperature, adding substantial superheat. Ever feel the bottom of a hand tire pump while someone pumps air with it? The discharge pressure of the compressor must be high enough so that after the air handler/condenser takes out the superheat, cooling the vapor down to the vapor pressure curve, the ensuing condensation takes place at a temperature somewhat above that of the air blowing past the other side of the coil. Again, "somewhat above" is a tradeoff between cost of coil surface area and energy cost of compression. The high pressure condensed refrigerant liquid returns to the evaporator coil (outside in the winter) to repeat the cycle.The amount of heat thus dumped to the destination (inside for heating season) is the amount of heat absorbed at the source plus the amount of energy provided by the compressor. The coefficient of performance (COP) for heating mode is the total delivered energy divided by the energy input by the compressor. This is typically in the range 2-3, although ground source heat pumps now go as high as 5. It takes more energy to lift an amount of heat from a colder outside temperature, so the COP drops as the outside temperature drops.The amount of heat that moves from outside air to the evaporating refrigerant is a matter of temperature difference between air and refrigerant and the surface area available for the heat transfer. At some cold outside temperature, there isn't enough surface area to move the heat required to evaporate all the refrigerant, and as the air temperature drops to the refrigerant temperature the heat transfer stops completely. Backup heat is required.Heat pumps designed for moderate climates just won't perform at colder outside air temperatures. There are cold climate heat pump designs that do work at air temperatures well below zero, with two-stage compressor operation and enhanced automatic defrosting.Bottom line then: yes, the amount of refrigerant in the system is critical. Specifically, the compressor suction side and discharge side pressures must be within mfg specs, so that the refrigerant can evaporate below the temperature of the outside air and condense above the temperature of the inside air. If the technician knows his stuff, he adds (or removes) refrigerant so that the gauges both are what the mfg literature says they should be for the particular system installed. Too little and the discharge pressure isn't high enough to provide a high enough condensation temperature. Too much and the evaporation temperature is too high, and not enough heat is absorbed in the evaporator coil outside.(Geez, do I dare post this long-winded bit of oration? Oh, heck, I can take the flame, I guess; a little flame is welcome in winter).

1. 
   roger g | Jan 17, 2008 12:00am | #6

   I actually know what you are talking about but a bit technical for most to understand.

   Refrigeration is very technical but I try to dumb it down till itactually makes sense even to me:)

    

   roger

2. 
   Syma | Jan 18, 2008 06:18pm | #7

   Hey everyone who responded here,
   a BIG thank you for your time.All seems fine for now until I can afford to upgrade to a York 8T series.Bye